A life of a rolling bearing varies due to a variety of complexly intertwined factors such as a material, a form, a size, a lubricant state, and a load of a bearing ring or a rolling element of the rolling bearing. Accordingly, in order to obtain the rolling bearing which has an appropriate durability according to use, it is necessary to perform a testing in order to know effects which the various factors exert on the life of the rolling bearing. FIG. 7 illustrates a radial rolling-bearing testing device in an example of the related art (for example, refer to Patent Document 1). In the radial rolling-bearing testing device, a leading end section (the left end section in FIG. 7) and a portion near to a base end of a rotary shaft 2 are rotatably supported inside a fixed housing 1 by a pair of radial rolling bearings 3 and 3 which each are bearings to be tested. A movable housing 4 is disposed concentrically to the rotary shaft 2 in a periphery of a center section of the rotary shaft 2 which is positioned between the radial rolling bearings 3 and 3. The movable housing 4 is provided inside the fixed housing 1 in a state in which a displacement in the radial direction is possible and a displacement in a rotation direction is prevented. Then, a support bearing 5 is provided between an inner peripheral surface of the movable housing 4 and an outer peripheral surface at the center section of the rotary shaft 2. Then, lower half sections of the support bearing 5 and the radial rolling bearings 3 and 3 are immersed in lubricant which is retained in a lubricant reservoir 6 that is provided inside the fixed housing 1. According to the need, foreign matters 7 and 7 such as metal powders and ceramic powders are mixed into the lubricant. A radial load F with a desired value which faces a vertical direction (up-and-down direction in FIG. 7) is freely applied to the movable housing 4 by a pressurizing device such as a hydraulic cylinder.
In a case where a life testing of the radial rolling bearings 3 and 3 is performed, the radial rolling bearings 3 and 3 are pressed in the vertical direction via the movable housing 4, the support bearing 5, and the rotary shaft 2 by pressing the movable housing 4 using the pressurizing device, and the rotary shaft 2 is driven so as to rotate. As a result, the life testing for durability evaluation of the radial rolling bearings 3 and 3 can be performed in a state in which the desired radial load F is applied and rotated at the desired rotation speed. In a case where the life testing of the radial rolling bearings 3 and 3 is performed using such a radial rolling-bearing testing device as described above, it is important to secure a circulation of the lubricant inside the lubricant reservoir 6, and uniformize characteristics such as an oil temperature of lubricant inside an entirety of lubricant reservoir 6.
Here, in a case of such a radial rolling-bearing testing device as described above, in order that the evaluation is performed with high reliability, it is important to sufficiently increase a rigidity of the fixed housing 1. That is, in a case where the rigidity of the fixed housing 1 is insufficient, there is a possibility that a portion of the fixed housing 1 which supports the radial load F deforms (elastically deforms). Thereby, there is a possibility that it is not possible to normally apply the radial load F to the radial rolling bearings 3 and 3 which are bearings to be tested, and a variance of test results is increased.
FIG. 8 illustrates a radial rolling-bearing testing device in a second example of the related art. In a fixed housing 1a with a rectangular box form which is open upward, a pair of side plate sections 9 and 9 which are parallel to each other, and a pair of end plate sections which connect end sections of the side plate sections 9 and 9 are formed so as to be supportedly fixed to an end plate section 8 with a flat plate form by respective welds and the like. When the life testing of the radial rolling bearing 3a is performed by the radial rolling-bearing testing device which includes with the fixed housing 1a, according to rotations (revolutions) of balls 10 and 10 of the radial rolling bearing 3a, the lubricant inside the lubricant reservoir 6a, which is provided inside the fixed housing 1a, is caused to flow in a same direction as a rotation direction of each of the balls 10 and 10. In the case of the second example of the related art, it is easy for the lubricant to be stagnated at corner sections (portions which are enclosed by a dotted line a in FIG. 8) close to a boundary of an upper surface of the bottom plate section 8 and an inner side surfaces of the side plate sections 9 and 9. As a result, there is a possibility that properties of the lubricant are not uniformized inside the lubricant reservoir 6a. In particular, in a case where the foreign matters 7 and 7 are mixed into the lubricant, there is a possibility that the testing is not performed with high reliability since the foreign matters 7 and 7 are stagnated in the corner sections, and it is not possible to appropriately feed the foreign matters 7 and 7 to the load zone of the radial rolling bearing 3a which is a bearing to be tested.